Notes, Notings, and Common Refrains

<3 Muppets.

I find the idea of Vikings having difficulty with English plurals very peculiar, must admit, though who am I to doubt? The thing is: Old Norse plurals have root vowel changes, too. Really, words that preserve those changes such as man/men might have more to do with similarity to the Old Norse than with repetition: frex, nominative singular maðr goes to nom. plural menn.

Then there are the words where you ask, "What are you doing, Old Norse? Why?" Example: saga to sǫgur, and the asshole adjective annar, which I'm going to provide the whole declension of because of all the pain I went through to recognize this particular word:
(N. = nominative, A. = accusative, G. = genitive, D. = dative, and I've stacked things such that singular/plural.)
Masculine:
N: annarr/aðrir
A: annan/aðra
G: annars/annarra
D: ǫðrum/ǫðrum

Feminine:
N.: ǫnnur/aðrar
A: aðra/aðrar
G: annarrar/annarra
D: annarri/ǫðrum

Neuter:
N.: annat/ǫnnur
A.: annat/ǫnnur
G.: annars/annarra
D.: ǫðrum/ǫðrum

Of course, if you go into the history all of those changes in sound make sense, and there are markers that help indicate gender/case, but knowing there's a reason for things doesn't make it easier to remember what's what.

[A side note: I'm wondering how consistent it is across languages that neuter nouns and adjectives take the same form in the nominative and accusative; Ancient Greek does the same.]